DE 197 02 854 A1 has already indicated that the individual driven grinding rollers are on one hand coupled to one another in the manner of a rotary drive via the grinding plate and the grinding stock or grinding stock bed located thereon and, on the other hand, can have very different power demands, which are for example due to different rolling diameters on the grinding plate (friction/diameter), different effective diameters of the individual grinding rollers (e.g. through wear) and a different behavior during draw-in of the grinding stock in the cooperation between grinding plate and grinding roller.
Even small changes in rotational speed between individual grinding rollers cause relatively large power variations in the individual drives. This can mean that the grinding rollers are constantly being accelerated or slowed, i.e. the individually driven grinding rollers work against one another, which leads to a substantially higher energy demand during comminuting operation.
DE 197 02 854 A1 therefore proposed equalizing the operating variations between the individual rotational drives of all the driven grinding rollers by means of a common load compensation control.
However, in the case of dynamic changes in transmission between grinding plate and grinding roller, the power demands of the drives are very different. In order to improve the compensation control, in DE 10 2007 006 092 A1 the compensation control consists of a power compensation control, wherein controlling the rotational speed of at least one drive controls the power of the drives in a predefined ratio to one another. According to DE 10 2007 041 878 B4, instead of controlling the rotational speed, the grinding pressure is controlled in order to control the power of the drives in a predefined ratio to one another.
DE 1 763 432 A further discloses a control device for a mill driven by a three-phase electric motor, for automatically controlling the supply of grinding stock for a constant load on the three-phase electric motor. EP 0 180 814 A2 discloses a roller mill with a control system in order to operate the mill over a broad throughput range, which ensures a satisfactory air-solid ratio and a desired degree of fineness.